Fading brakes whilst driving on corrugations

[MEGATROL]

I have a problem in my 92 GQ wagon, for every day driving my brakes seem to work fine on and off road, but as soon as I drive a section of corrugations for more than 5 or so seconds I go to ease the brakes to slow down and the pedal nearly hits the floor.
It takes a good three pumps to get bake to a hard pedal, but as soon as I get back onto smooth section of road it's all good again. I have tried bleeding the system more than once

Any ideas what could cause this????

pickels

[76 Tourer]

Check wheelbearing adjustment, can get some pad knockback if they are loose .

[Lepa]

yep have the same issue, so interested in any input others have. going to try a few things and if any work i'll post up

lepa

[V8Patrol]

Check wheelbearing adjustment, can get some pad knockback if they are loose .

x2


add to your check list......................

loose brake calipre/components .... worn/warped brake disc .... and in the case of drums brakes check adjustment and drum warpage.

[MEGATROL]

Hi thanks for the replys
The wheel bearings have been checked more than once as that was my first idea.
And if it had warped discs it would happen all the time but it's only happening on corrugated roads only.

Any more ideas out there???

[76 Tourer]

Had these issues with the work cars when I was an apprentice ... major contributer was the bearings but have a hazey recollection of rebuilding the calipers as well to solve the problem . Thinking about it ... sort of makes sense vibrating pad pushing pistons back in due to worn seals .

Might be worth a try

edit: were there stainless shims or something that the pad sits on between the caliper housing and pad that are missing ? allowing the pad to move ...

Like I said hazey

[GUtripper]

Strange, my post disappeared............

How about a cracked or damaged vaccum line to the booster? Over rough roads the line flexes losing vaccum, = less power to brakes?

[76 Tourer]

^^^^ worth a look but I would have thought that that would make the pedal hard not travel to the floor

[MEGATROL]

Yeh thanks 76 tourer I mite look into rebuilding the calipers in the near future, and as you said broken vacuume line would create a hard pedal not send it to the floor so that kinda rules that out

Thanks for your help everyone I'll look into redoing th calipers with a new set of discs and see how that goes

[MikeH]

Disc brake rear?
I bet you have a stuffed bearing in the back then.

[MEGATROL]

Yes it is a disc brake rear but like I said if it was a bearing on the front or rear it would have the problem all the time but it's only on corrugated roads

[oldmate]

If the pedal is going to the floor you have a hydraulic problem. My guess would be the master cylinder.